Database Systems vs. Files and DBMS Characteristics
What is a DQL?
- DQL = used to INTERROGATE the database - Retrieves, sorts, orders, presents subsets of the database in response to user queries - Example is SQL
What is a DML?
-DML = Data manipulation language -Update, insert, delete portions of the database -Usually a verb
What are the two components of a DBMS?
1. Data Dictionary 2. DBMS Languages
Define DBMS
-Program that MANAGES and CONTROLS ACCESS to the database -Defines data structures for an IT application -DBMS controls the database so that users can access, query, or update it without reference to how or where the data are physically stored
What is a DBMS language used for?
-The sets of commands used to do three things: CREATE, CHANGE, and QUERY the database -Types of DBMS languages are called data definition language, data manipulation language, and data query language
What is a tuple?
Each row in a relation
What are the three levels of schemas?
1. Conceptual level schema 2. External level schema 3. Internal level schema
What are the problems with file-based approaches?
1. Duplication of data 2. Specific data values stored in different files are not consistent
What is a Data Dictionary?
A read-only set of tables that provides information about the database, containing: - definitions of schema objects - rights of access for each user - information about who has accessed or updated schema objects - how much space allocated for schema objects - names of users
How is the logical and physical view of data different?
AKA "Program-data independence" -Logical = how programmer conceptualizes data -Physical = how it is physically arranged and stored on disk, tape, CD, or other media
Define conceptual-level schema
An organization-wide view of the entire database
Define a database system
Combination of 1. the database 2. the DBMS 3. and application program that uses the database
Define external-level schema
Consists of a set of individual user views of PORTIONS of the database (also called a subschema)
What are advantages to the database approach?
Controlled data redundancy, consistent data, integrated data, shared data, eases application development
What is a DDL?
DDL = Data definition language Used to build the data dictionary and create the database
Define an internal-level schema
Provides a low-level view of the database
What is a schema?
Schema describes logical structure of a d.b.
SQL
Structured Query Language -a standard query language for requesting information from a database (DQL)